The term “piezoelectric direct drive” used here is intended to comprise in this context driving without a servo valve, or purely mechanical driving, for example by means of a lever system, or driving with a hydraulic transmission means.
In such a drive, the nozzle needle of the injector is accelerated strongly after the opening, with the result that when there is a mechanical impact of the nozzle needle (in the case of a mechanical drive system) or when there is a hydraulic equilibrium point (in the case of a hydraulic equilibrium system), the nozzle needle oscillates a few times and brings about a characteristic curve ripple. As a result, the quantity accuracy in this range is reduced.
In order to eliminate this problem, in the case of mechanical drive systems it has been attempted to detect the corresponding impact point and to avoid this range for implementation of the injection time.